Gate valves are used in oil and gas industry for a variety of flow lines. A typical gate valve has a body with a central cavity. The body has two passages that are coaxial and intersect the central cavity. Seat rings are located at the junctions of the flow passages with the central cavity. A gate is moved past the seat rings to either open or close the flow passages.
The gate valves of the type concerned herein are designed so that the downstream gate will form a metal-to-metal seal with the downstream seat ring. The downstream seat ring also has to seal to the counterbore within the body in which it is located. Metal and elastomeric seal rings have been utilized in the past to seal the seat rings in the counterbores. Also, it is known to press seat rings within the counterbores to form an interference fit that is sufficiently tight so as to form a seal.
In high temperature applications, elastomeric seals and some metal seal rings may not be usable. Interference fit sealing will normally withstand high temperatures, however, pressing the seat rings into the counterbores is difficult. It is not easy to maintain alignment and avoid cocking of the seat ring relative to the counterbore.